This invention relates to a novel method for the disposal of dusts from incinerator plants.
A process is known for the disposal of salt-containing dusts from garbage incinerator plants by the German patent DE-OS 3734 879, wherein, with the addition of water, the salt-containing dusts are mixed intensively with other waste materials, such as ash and fly ash from thermal power plants fired with brown coal (lignite) or hard coal, silica containing sands, waste rubble, or waste materials from calcium carbide production. The mixture contains at least 8% hydrothermally reactive calcium oxide or equivalent amounts of other hydrothermally reactive compounds, and the water admixture is so rated that an optimum compaction is possible. The mixture is thereafter processed by compacting the mixture into rigid compacts. The compacts are subsequently hardened in an autoclave by saturated steam with a pressure of at least 1 bar.
This known process for the treatment of salt-containing dusts from flue gas cleaning plants, using the dry or semi-dry process, is unsuitable for the processing of dust from incinerator plants. The inadequacy is due to the small quantities of or absence of hydrothermally reactive calcium hydroxide in the salt-containing dusts.
The cleaning of the flue gas from incinerator plants is accomplished in at least two steps: in one stage, all solid detrimental materials are separated and, in a second stage, the gaseous materials are removed by the addition of water or water and chemicals. The removal of solid particles, which are also designated "dusts" or "fly ashes", is accomplished by bag filters or by electrostatic precipitators. Salt-containing dusts are obtained when the dry or semi-dry cleaning procedures are used for cleaning the flue gases from incinerator plants. These salt-containing dusts are a mixture of fly ashes and salts, in particular calcium sulfate, calcium chloride, and calcium fluoride or the hydrates of these salts.
It is common practice to inject quick lime or pulverized limestone into the combustion chamber in order to reduce the content of sulfate and chloride in the flue gas. Due to this practice, the content of the sulfate, chloride, and free quick lime are increased in the fly ashes. The content of free lime in these dusts originates from a surplus of injected lime which does not react with the sulfates and the chlorides contained in the flue gases.
A procedure for the treatment of dusts from incinerator plants is known wherein the dusts are mixed with cement and a quantity of water that produces a crumbling mass of low water content. The mixture is transported to a landfill and is compacted through the use of the usual ground compacting equipment. After compaction, the dust-cement mix cures in the usual way in situ. The disadvantage of this procedure is that the relatively large content of free hydrated lime in the mix results in a high pH value and therefore a high solubility of lead. Consequently, it is obligatory to dispose of the material in a specially classified landfill, and it is also impossible to use such materials as aggregates for concrete.